I wish I could find this information for LFP batteries. There’s a lot out there, but it’s all mixed with advice for LiPo; I can’t find anything I trust to tell me the optimal voltages for maximum lifetime.
For general advice, they like it cooler[1] than other kinds of lithium batteries. Try to keep them between 15-25°C. Other than that, charge LFP batteries to whatever percentage you want whenever you want.
They are simply better than every other kind of lithium chemistry. Their practical downside is lower cell voltage (3.2 vs 3.8), and slightly lower energy density. I've spent the last 7 years building LFP-powered lawnmower-sized robots, and in practice, the lower voltage and doesn't matter. And, unlike other chemistries, they don't catch fire when you stab them.
For other kinds of lithium batteries, to maximize lifetime, keep them between 40-60%, avoid big charge swings (10-90%), and keep them warm (above 25°C).
[1]: At 35°C, tests show they lose about 5% more capacity after 2,000 cycles compared with 25°C. But even that isn't really a problem, because they don't get to 20% capacity loss until 4,000 cycles. See: https://iopscience.iop.org/article/10.1149/1945-7111/abae37, fig 3.
It’s also unused for half the year, and for much of that half the solar input is effectively zero; for part it’s literally zero. Not enough to even run the Victron gear, never mind a heater. Spring temperatures often drop below -5C.
So we’ll winterise it by shutting everything off, BMS included to the degree it’ll let us, and the question is what SoC they sold be at for that to work.
Also, I wouldn't worry about the BMS too much. Unless it's really dumb, when there's no charging or discharging happening it will put itself to sleep for most of that time. Technically it will use power, but likely only a few hundred micro watts to a few milliwatts (nothing that will make a difference on a 5 kWh+ battery). Then when the sunlight comes back in the spring (or whenever the snow melts off the solar panels), it'll see some input voltage and start feeding the battery again.
Even though a lower voltage prolongs the battery, you have to charge to 100% regularly to help the BMS. Thankfully the LFP chemistry doesn’t seem to mind high state of charge as much.
As a popular source, Tesla recommends to daily charge the LFP batteries to 100%.
That's a weird statement. The voltage curve for LFP [0] is just a lot flatter. That's nice for your electronics, but makes it hard to estimate state of charge based on the voltage alone. So the BMS needs to keep track of total energy used to calculate state-of-charge.
[0] https://www.jackery.com/blogs/knowledge/ultimate-guide-to-li...
When an individual cell reaches a set voltage, a resistor is turned on which bleeds the excess power preventing that cell from overcharging. When the pack reaches 100% theoretically every cell should then be at the same voltage.